Using Boulder Tracks as a Tool to Understand the Bearing Capacity of Permanently Shadowed Regions of the Moon

Abstract

Permanently shadowed regions (PSRs) are abundant at the lunar poles. They experience no direct sunlight and reach temperatures as low as 30 K. PSRs are of interest as evidence suggests that some may contain water ice (H2O/OH‐), which could provide a record of the evolution of volatiles in the inner solar system. This water ice is also a critical resource for life‐support systems and rocket propellant. A better understanding of mechanical properties of PSR regolith, such as its bearing capacity, will help optimize the design of future exploration rovers and landers. Thirteen boulder tracks were identified on the edge of, or inside, south polar lunar PSR enhanced imagery and used to estimate the strength of the PSR regolith at latitudes of 70° to 76° in sites with maximum annual temperatures of 65 to 210 K. PSR boulder track features are similar to those observed in highland, mare, and pyroclastic regions of the Moon, implying similar properties of the regolith. Measured features were used to estimate bearing capacity for PSR regolith at depths of ~0.28 to 4.68 m. Estimated bearing capacity values suggest that these PSRs may be somewhat stronger than highland and mare regions at depths of 0.28 to 1.00 m. Bearing capacity in these PSRs is statistically the same as those in other regions of the Moon at depths of 1.00 to 2.00 m. The results of this study can be used to infer bearing capacity as one measure for the trafficability of lower‐latitude PSRs of the type measured here.

Deep Learning-Driven Detection and Mapping of Rockfalls on Mars

“…Besides their implications for weathering processes and seismic activity of Mars, rockfalls and their tracks can be used to infer the mechanical properties of regolith, as demonstrated on the Moon by e.g. [30] during the Apollo era and recently by [22][23], directly informing future surface exploration efforts. A deep learning-enabled global study of rockfall distribution on Mars could provide valuable information for a wide variety of relevant scientific and exploration-related applications.…”

“…Thus, suspected regions of increased seismic activity inferred from rockfall frequency patterns could be priority targets for the deployment of future geophysical networks. The tracks created by extraterrestrial rockfalls, i.e., boulder tracks, are also a valuable tool to estimate the basic mechanical properties of the surface substrate present [22][23]. However, the manual detection and mapping of martian rockfalls (boulders with tracks, here also called feature of interest) in satellite imagery remains a challenging task.…”

Impacts drive lunar rockfalls over billions of years

“…Past studies have mapped lunar rockfall features for selected regions across the lunar equatorial and polar highland, mare, pyroclastic, and permanently shadowed regions [7][8][9]14,15 . These studies have hypothesized that the main drivers of lunar rockfalls are shallow and deep moonquakes, impact-induced shaking, and thermal fatigue caused by the extreme temperature variations on the Moon 7,16 .…”

Global Drivers and Transport Mechanisms of Lunar Rockfalls

“…The tracks of displaced boulders were used to estimate some of the geomechanical properties of the lunar regolith in preparation of the Apollo missions (e.g., Hovland & Mitchell, 1973;Moore, 1970). More recently, lunar rockfall tracks mapped in NAC imagery have been used to estimate geomechanical properties of regions of increased exploration interest, such as large pyroclastic deposits (Bickel et al, 2019), sunlit south polar regions (Bickel & Kring, 2020), and south polar permanently shadowed regions (Sargeant et al, 2020).…”